1. Field of the Invention
The present invention relates to an electrolytic solution for use in an electrolytic capacitor which includes a conductive separator formed with a conductive polymer layer on its surface, and an electrolytic capacitor using the same.
2. Prior Art
As various electronic devices require higher frequencies, the demand for a large-capacity electrolytic capacitor having excellent equivalent series resistance (hereinafter also referred to as ESR) characteristic at high frequency areas has grown.
In recent years, as the aforementioned electrolytic capacitor, there has been proposed an electrolytic capacitor having a structure in which a conductive separator formed with a conductive polymer layer on its surface is interposed between a pair of electrodes.
For example, Patent Exhibit 1 below proposes to improve the ESR characteristic by giving electric conduction to the separator of the electrolytic capacitor by means of a conductive polymer.
On the other hand, there has conventionally been developed an electrolytic solution for electrolytic capacitor (hereinafter, also simply referred to as an electrolytic solution) for reducing the energy loss or improving the ESR characteristic of the electrolytic capacitor. As such an electrolytic solution, an electrolytic solution having high electric conductivity has been proposed. Specific example thereof is a so-called amidine-based electrolytic solution such as described in Patent Exhibit 2. This electrolytic solution contains carboxylic acid salt of a quaternary compound having alkyl-substituted amidine groups as an electrolyte. However, the use of only said electrolytic solution having high electric conductivity is still insufficient to improve said ESR characteristic and the like.
In an attempt to further reduce the energy loss and improve the ESR characteristic, the present inventors employed the amidine-based electrolytic solution such as described in Patent Exhibit 2 to the electrolytic capacitor having the ESR characteristic which has been improved by giving conduction to the separator such as described in Patent Exhibit 1 by means of a conductive polymer. However, there arose a problem that the ESR of the electrolytic capacitor increased.
[Patent Exhibit 1] Japanese Unexamined Patent Publication No. 1-90517
[Patent Exhibit 2] International Unexamined Patent Publication No. 95/15572, pamphlet